How far? the extent of chemical change: notes and practice questions

Nitrogen monoxide is formed from nitrogen and oxygen in internal combustion engines according to the following equilibrium:

$N_2(g) + O_2(g) \rightleftharpoons 2NO(g) \quad \Delta H = +180 \text{ kJ mol}^{-1}$

What is the effect on the value of the equilibrium constant, $K_c$, when the temperature of the system is decreased?

A. It will increase.

B. It will decrease.

C. It will remain the same.

D. It is impossible to determine without knowing the change in pressure.

What is the pH of a buffer solution prepared by mixing $0.300 \text{ mol dm}^{-3}$ propanoic acid ($CH_3CH_2COOH$) and $0.450 \text{ mol dm}^{-3}$ sodium propanoate ($CH_3CH_2COONa$)?

The $pK_a$ for propanoic acid is $4.87$.

A. $4.69$

B. $4.87$

C. $5.05$

D. $5.23$

In an industrial process for ammonia synthesis, nitrogen gas reacts with hydrogen gas according to the following reversible equation:

$N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$

A mixture of $1.50\text{ mol}$ of $N_2(g)$ and $4.00\text{ mol}$ of $H_2(g)$ was introduced into a $1.00\text{ dm}^3$ reaction vessel at a constant temperature. When the system reached equilibrium, the amount of $N_2(g)$ present was $0.90\text{ mol}$.

Which expression represents the value of the equilibrium constant, $K_c$, for this reaction?

A. $\frac{(1.20)^2}{(0.90)(2.20)^3}$

B. $\frac{(1.20)^2}{(0.90)^3(2.20)}$

C. $\frac{(0.90)(2.20)^3}{(1.20)^2}$

D. $\frac{(1.20)}{(0.90)(2.20)}$

An industrial chemist is monitoring the synthesis of ammonia via the Haber process, represented by the following equilibrium reaction:

$N_2 (g) + 3H_2 (g) \rightleftharpoons 2NH_3 (g)$

At a particular temperature, the equilibrium constant, $K_c$, for this reaction is $0.50$.

In a reaction vessel, the chemist measures the following concentrations:

$[N_2] = 0.10 \text{ mol dm}^{-3}$

$[H_2] = 0.20 \text{ mol dm}^{-3}$

$[NH_3] = 0.050 \text{ mol dm}^{-3}$

Which statement correctly describes the state of the system and the direction it will shift to reach equilibrium?

A. The system is at equilibrium, and the rates of the forward and reverse reactions are equal.

B. The forward reaction rate is favoured to establish equilibrium.

C. The reverse reaction rate is favoured to establish equilibrium.

D. The system is not at equilibrium, but no net reaction will occur.

A chemical engineer is optimizing the conditions for the industrial synthesis of ammonia via the Haber process. The reaction is carried out in a sealed vessel at a constant temperature of $673\ K$.

At equilibrium, the concentrations of the reacting species are measured as follows:

$[N_2(g)] = 0.20\text{ mol dm}^{-3}$

$[H_2(g)] = 0.10\text{ mol dm}^{-3}$

$[NH_3(g)] = 0.40\text{ mol dm}^{-3}$

What is the value of the equilibrium constant, $K_c$, for the reaction $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$ at $673\ K$?

A. 8

B. 20

C. 800

D. 2000